Header: Mainframe header redesign (#363)

* Header: Mainframe header redesign

Restyle coveo search box
Restyle F5 Sites button
Move search box to left side
Move sidebar toggle to main header
Move product selector to sidebar

* Header: Hide sidebar controls on pages without a sidebar

Applies to 404, search, and homepage

* Header: Center header logo horizontally regardless of flow

* Sidebar: Move search to top of mobile view, remove selector

* Header: Fix sidebar action icon mismatch on mobile

* ProductSelector: New product selector

* ProductSelector: Show selected product

* ProductSelector: Show selected product

* Header: Adjust product selector styling

* Sidebar: Adjust Coveo styling to better match product selector

Applies to mobile

* Sidebar: Position collapse button within sidebar on mobile

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Co-authored-by: Michael McKeen <[email protected]>

Author: nginx-jack